Subsetting from a dataframe in R

Question

I have sampled 'n' rows from a dataframe called nodes:

nodes <- structure(list(node_number = 1:50, 
                        x = c(2L, 80L, 36L, 57L, 33L, 76L, 77L, 94L, 
                              89L, 59L, 39L, 87L, 44L, 2L, 19L, 5L, 
                              58L, 14L, 43L, 87L, 11L, 31L, 51L, 55L, 
                              84L, 12L, 53L, 53L, 33L, 69L, 43L, 10L, 
                              8L, 3L, 96L, 6L, 59L, 66L, 22L, 75L, 4L, 
                              41L, 92L, 12L, 60L, 35L, 38L, 9L, 54L, 1L), 
                        y = c(62L, 25L, 88L, 23L, 17L, 43L, 85L, 6L, 11L, 
                              72L, 82L, 24L, 76L, 83L, 43L, 27L, 72L, 50L, 
                              18L, 7L, 56L, 16L, 94L, 13L, 57L, 2L, 33L, 10L, 
                              32L, 67L, 5L, 75L, 26L, 1L, 22L, 48L, 22L, 69L,
                              50L, 21L, 81L, 97L, 34L, 64L, 84L, 100L, 2L, 9L, 59L, 58L), 
                        node_demand = c(3L, 14L, 1L, 14L, 19L, 2L, 14L, 6L, 
                                        7L, 6L, 10L, 18L, 3L, 6L, 20L, 4L, 
                                        14L, 11L, 19L,  15L, 15L, 4L, 13L, 
                                        13L, 5L, 16L, 3L, 7L, 14L, 17L, 
                                        3L, 3L, 12L, 14L, 20L, 13L, 10L, 
                                        9L, 6L, 18L, 7L, 20L, 9L, 1L, 8L, 
                                        5L, 1L, 7L, 9L, 2L)), 
                   .Names = c("node_number", "x", "y", "node_demand"), 
                   class = "data.frame", row.names = c(NA, -50L))

To sample I use this code:

hubs <- nodes[sample(1:total_nodes, hubs_required, replace = FALSE),]

Which returns :

node_number  x  y node_demand
33          33  8 26          12
14          14  2 83           6
42          42 41 97          20
13          13 44 76           3
10          10 59 72           6

I would like to return all the rows that haven't been selected so that I can perform a series of calculations on them.

I thought that using something like data[-sample,] would work but I get the following error

Error in xj[i] : invalid subscript type 'list'.

Anybody know who could I get these values?

When asking for help, you should include a simple [reproducible example](https://stackoverflow.com/questions/5963269/how-to-make-a-great-r-reproducible-example) with sample input and desired output that can be used to test and verify possible solutions. Did you literally try `data[-sample,]`? Did you create a variable called `sample` or were you trying to call the `sample()` function there? — MrFlick, Jun 14 '18 at 19:22
I have updated the code, I hope it looks clearer now. I saved the results from the `sample()` function in the hubs variable. — Sergi, Jun 14 '18 at 19:28
Yes, I thought it would work since `data[-sample,]` does work with matrices, but unfortunately it's not the case with dataframes. — Sergi, Jun 14 '18 at 19:31

score 2 · Accepted Answer · answered Jun 14 '18 at 19:32

2

It would be easier to keep the list of indexes that selected. Somthing like

hubs <- nodes[keep <- sample(1:total_nodes, hubs_required, replace = FALSE),]
other_hubs <- nodes[-keep, ]

Otherwise, if your data has some sort of key/ID, you can do something like

other_hubs <- nodes[nodes%node_number  %in%  hubs$node_number, ]

or with dplyr, this can be an anti-join

nodes %>% anti_join(hubs, by="node_number")

answered Jun 14 '18 at 19:32

MrFlick

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Thanks! The first one worked well!. I am surprised that although the syntax was the same i.e `nodes[-keep,]` It didn't throw the error message. Is it because the variable was initialized as a subset? `nodes[keep <- sample(1:total_nodes, hubs_required, replace = FALSE),]` I've never seen that way of doing it before :) – Sergi Jun 14 '18 at 19:37

Subsetting from a dataframe in R

1 Answers1